1. The cell center (the microtubules organizing centers (MTOC) and the centrioles) was reconstructed from electron micrographs of serial sections and was found to be highly organized in the pigment cell of Holocentrus. This center is implicated in forming and maintaining the cell shape and its filamentous systems. 2. The organization of the endoplasmic reticulum (ER) and the Golgi apparatus in arcuate nucleus neurons of the hypothalamus was studied. Part of the ER, or whorlbody, was reconstructed and found to resemble a combination of rough and smooth ER, which at some points is related geographically to the Golgi apparatus. A small pilot project of the structure of the Golgi apparatus in CHO cells has been initiated. The significance of our findings is that it will allow us to follow the mechanism of ER shape changes and its relation to the Golgi apparatus. 3. Many sections of rat brain were digitized and processed for developing a single full stereotaxic representation of the whole brain. We have initiated the steps that will allow us to represent the projection of neurotransmitters, peptides and receptors in color in their respective locations. 4. We digitized many sections of mouse embryos at different stages of development and initially processed them and are ready now for their three dimensional reconstruction. This will be used to evaluate the effects of teratogens and to follow the migration of germ cells in embryos. These studies were made feasible by the development of a high resolution computer graphics system for three dimensional reconstruction. Algorithms and programs were devised to digitize serial sections, to align them and reconstruct them into a single three dimensional image. The significance of these studies is that they will further our understanding as to how the cell gains its shape, and organizes its organelles and the tissue studies will reveal new functional interrelationships in the brain and embryos.